1. Field of the Invention
The present invention relates to a semiconductor structure and the manufacturing method thereof, in particular, to a semiconductor structure applied in SONOS memory.
2. Description of the Prior Art
During the programming of a typical silicon-oxide-nitride-oxide-silicon (SONOS) memory, electrical charge is transferred from a substrate to the charge storage layer in the device, such as the nitride layer in the SONOS memory. Voltages are applied to the gate and drain creating vertical and lateral electric fields, which accelerate the electrons along the length of the channel. As the electrons move along the channel, some of them gain sufficient energy to become trapped in the charge storage dielectric material. This jump is known as hot carrier injection, in which the hot carriers are the electrons. Charges are trapped near the drain region as the electric fields are strongest near the drain. Reversing the potentials applied to the source and drain will cause electrons to travel along the channel in the opposite direction and be injected into the charge storage dielectric layer near the source region. Since parts of the charge storage dielectric layer are electrically conductive, the charged introduced into these parts of the charge storage dielectric material tend to remain localized. Accordingly, depending upon the application of voltage potentials, electrical charge can be stored in discrete regions within a single continuous charge storage dielectric layer.
However, the ability for trapping and retaining electrical charges under current SONOS architecture is still not perfect, including shortcomings such as insufficient trapping sites for charges as well as easy leakage. Hence how to effectively improve the current SONOS architecture to increase the overall performance of the device has become an important task in this field.